Double-layer-structure cold-pressed pellet based on gradient binder and preparation method of double-layer-structure cold-pressed pellet

Abstract

The invention relates to a double-layer structure cold-pressed pellet based on a gradient binder and a preparation method of the double-layer structure cold-pressed pellet. The method belongs to the technical field of cold-pressed pellet forming. Aiming at the technical bottleneck that the production cost is high due to the fact that a homogeneous structure of a traditional cold-pressed pellet needs to depend on a high binder addition amount to maintain the strength, the invention innovatively provides a cold-pressed pellet structure form with the inner layer and the outer layer being layered: the outer layer adopts a binder with a high proportion to form a compact compression-resistant shell, and the inner layer forms a supporting core body by reducing the binder content. By regulating and controlling the gradient distribution of the binders on the inner layer and the outer layer, the overall compressive strength is guaranteed, meanwhile, the total dosage of the binders is remarkably reduced, and the high dependence of a traditional homogeneous structure on the binders is broken through. The structural design is adaptive to a conventional cold pressing process, low-cost and high-efficiency production can be realized without complicated equipment modification, and the structural design has remarkable economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of cold-pressed pellet forming, and specifically relates to a double-layer cold-pressed pellet with a gradient binder and a preparation method thereof. Background Art

[0002] The steel industry accounts for approximately 15% of global CO2 emissions and produces a large amount of iron-containing solid waste. In China, sintered ore and pelletized ore dominate the blast furnace-converter (BF-BOF) process. However, due to challenges such as poor iron ore quality and environmental pressure, a green and low-carbon transformation and upgrading of steel charge materials and their preparation technologies is imperative. Unlike sintered ore and pelletized ore, cold-pressed pellets are a common technology for pre-treating powdered metallurgical raw materials (such as iron ore powder and coke powder). They use external forces to break the "arch bridge effect" caused by friction and mechanical interaction between particles, promote favorable arrangement of particles, and effectively improve the efficiency of raw material transportation and the reduction reaction rate during the smelting process through cold pressing of binders and materials.

[0003] Cold-pressed pellets have metallurgical adaptability in multiple scenarios. They can be used as metallized charge for blast furnace smelting to improve the molten iron yield through direct reduction reaction. They can also be used as coolant and heat supplement medium for converter steelmaking to replace part of scrap steel or iron ore, thereby realizing dynamic heat balance regulation of the steelmaking process. At the same time, the cold-pressed pellets can absorb industrial solid wastes such as iron-containing dust and mud (such as sintered ash, converter OG mud), steel slag powder, etc. on a large scale (the mixing ratio can reach 30%-50%), reduce the consumption of natural mineral powder, and reduce carbon emissions per ton of steel by reducing the coke ratio, which is in line with the steel industry's carbon tax compliance cost control and low-carbon transformation needs.

[0004] In current cold-pressed pelletizing technology, binder costs constitute a significant bottleneck. Traditional homogeneous structures rely on a high proportion of binders (such as bentonite and organic resins) to meet industrial requirements for compressive strength, resulting in binder costs accounting for an excessively high proportion of the total pellet production cost. Furthermore, as the proportion of low-grade ores and complex solid waste increases, the demand for binder usage further increases. The addition of a high proportion of binder not only directly increases raw material costs, but also reduces pellet porosity due to excessive inorganic binder covering the surface of active minerals, hindering the diffusion of reducing gases within the blast furnace and indirectly increasing smelting energy consumption.

[0005] Existing optimization schemes mostly focus on binder modification (such as the method of CN103484665A using different binders and two-step pelletizing to produce metallurgical composite pellets) or pressing parameter adjustment, but none of them breaks through the rigid dependence of the homogeneous structure on high binder addition, and the cost reduction is greatly limited. Summary of the Invention

[0006] In view of the defects of the prior art, the present invention provides a double-layer cold-pressed ball block based on a gradient binder design and a preparation method thereof, so as to solve the technical problem that the binder cost of the existing cold-pressed balls is high due to the homogeneous structure.

[0007] To solve the above technical problems, the present invention adopts the following technical solution: a method for preparing double-layer cold-pressed pellets based on a gradient binder, comprising the following steps:

[0008] S1: Preparation of raw materials for pelletizing: The iron ore powder and industrial solid waste produced in the factory are crushed, sieved using a porous sieve, and particles with a size of less than 0.15 mm are selected as experimental raw materials, and then dried.

[0009] S2: Mix the raw materials, binder and water evenly: According to the different amounts of binder added in the inner and outer layers, the pelletizing materials are configured separately to form iron-containing mixtures, which correspond to material A and material B respectively.

[0010] S3: Layered ball making: The inner layer (I) uses material A, which is pressed into a cylindrical core on a press, and then half of material B is poured into an ellipsoidal mold. The cylindrical core is placed in the center of the material layer, and then the remaining material B is poured in. The green ball is obtained through a cold pressing process.

[0011] S4: Cold pressed pellet consolidation: The green pellets are placed at a certain temperature to dry and consolidate, and finally cold pressed pellets are obtained.

[0012] Preferably, in step S1, the selected raw materials are one or more of ball-milled iron powder, iron ore powder, dust removal ash, and iron oxide scale; and the selected binder is one or more of corn starch, sodium silicate, CMC, and bentonite.

[0013] Preferably, in step S2, when preparing the raw material for the inner layer (I), the amount of binder added is 2.2%-2.6% of the total mass of material A, and the amount of water added is 5.8%-6% of the total mass of material A. When preparing the raw material for the outer layer (O), the amount of binder added is 2.6%-3.0% of the total mass of material B, and the amount of water added is 5.9%-6% of the total mass of material A. The mixing time is 10-15 minutes. The amount of binder added to material A can be 2.2%, 2.4%, or 2.6%. The amount of binder added to material B can be 2.6%, 2.8%, or 3.0%.

[0014] Preferably, in step S3, during the cold pressing process, a linear pressure of 25-30 MPa is applied to the mold, and the holding time is maintained from 15±0.5s to 20±0.5s to promote mechanical engagement between powder particles and pre-curing of the binder to produce cold-pressed green balls.

[0015] Preferably, in step S4, the green pellets are placed in a constant temperature environment of 100°C±2°C for heat curing, and the curing time is controlled to be 24±0.5h, so that the binder is fully cross-linked and cured, and finally cold-consolidated pellets are obtained.

[0016] A double-layer cold-pressed pellet based on a gradient binder, which consists of a double-layer structure, including an outer layer using a high-proportion binder with a mass accounting for 2.6%-3.0% of the total mass of the outer layer to form a high-density compressive protective layer, and an inner layer using a low-proportion binder with a mass accounting for 2.2%-2.6% of the total mass of the inner layer to construct a porous supporting skeleton, thereby achieving coordinated optimization of structural strength and raw material costs.

[0017] The components of the two layers of adhesive include raw materials, adhesive and water, and the amount of adhesive added in the outer layer and the inner layer forms a continuous gradient distribution: the concentration gradient difference between the outer layer adhesive mass proportion of 2.6%-3.0% and the inner layer 2.2%-2.6% is 0%-0.8%.

[0018] Compared with the prior art, the present invention has at least the following advantages:

[0019] (1) The present invention realizes the concentration gradient difference between the outer layer (2.6%-3.0% binder) and the inner layer (2.2%-2.6% binder) through gradient heterogeneous structure design, and constructs a "dense outside and sparse inside" functionalized sphere: the high binder in the outer layer forms a dense pressure-resistant shell, which effectively resists the mechanical impact of transportation and smelting; the low binder in the inner layer constructs a porous support skeleton, which significantly accelerates the diffusion efficiency of the reducing gas.

[0020] (2) Based on the gradient structure optimization, the present invention significantly reduces the total binder dosage compared to the traditional homogeneous structure, breaking through the technical bottleneck of homogeneous pellets relying on high binder addition, while achieving the coordinated regulation of compressive strength, reduction reaction efficiency and raw material cost, providing a solution with both performance and economy for the industrial application of cold-pressed pellets. Based on this gradient design, by regulating the concentration distribution of the binder in the radial direction of the pellets, while maintaining the overall compressive strength of the pellets, the total binder addition amount is reduced by 8.44%-21.37% compared to the traditional homogeneous structure (3.0%-3.5%), for example:

[0021] Gradient binder layered structure cold pressed ball binder addition amount (the inner and outer layers are calculated based on the middle value):

[0022] 2.4%×10g+2.8%×65g=2.06g (1)

[0023] The amount of binder added to the traditional homogeneous cold-pressed ball (the mass is 75g, consistent with this experiment; the amount of binder added to the traditional cold-pressed ball is also the middle value of 3.25%):

[0024] 3.25%×75g=2.44g (2) Reduction in the amount of binder added:

[0025]

[0026] (3) The double-layer structure maintains strength through the gradient distribution of the adhesive:

[0027] 1) Outer layer high adhesive → build high strength outer shell (improve interface bonding + optimize stress distribution)

[0028] 2) Inner layer low adhesive → acts as a low stress buffer layer (low pressure environment in the core, forming a secondary stress zone)

[0029] 3) Physical synergistic effect: The solidification shrinkage of the outer layer forms prestressed protection for the inner core; the high-toughness surface layer inhibits crack initiation and propagation.

[0030] Essentially, the limited adhesive resources are prioritized in the most mechanically sensitive areas (the surface), reconstructing the stress field and failure path through physical interaction. This design reduces overall costs while still meeting the 2000N compressive strength requirement, demonstrating innovation in material-mechanics synergistic optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a cross-sectional view of a double-layer structure gradient cold-pressed ball. DETAILED DESCRIPTION

[0032] The present invention is described in further detail below.

[0033] The present invention provides a double-layer cold-pressed pellet based on a gradient binder and a preparation method thereof, the specific steps of which are as follows:

[0034] Step S1: Preparation of experimental raw materials.

[0035] Specifically, (1) crushing and screening: the iron ore powder and metallurgical solid waste are crushed to a particle size of ≤5 mm by ball milling, and then vibrated and screened through a 100-mesh (pore size 0.15 mm) standard sieve, and the undersize (particle size <0.15 mm) is collected as the basic raw material; (2) drying and water control: the raw materials obtained by screening are placed in a constant temperature drying oven, and continuously dried at a constant temperature of 100±2°C for 12±0.5h, and then cooled to room temperature (25±2°C) for use.

[0036] For the convenience of description, the iron ore powder used in the following examples has the following specific composition: Fe2O3: 85.47%, SiO2: 7.34%, Al2O3: 5.11%, MgO: 0.51%, MnO: 0.35%, P2O5: 0.21%, CaO: 0.20%, TiO2: 0.14%, and the rest are unavoidable impurities.

[0037] Step S2: Mixing the raw materials, binder and water.

[0038] Specifically, the iron ore powder used in the experiment was removed from the drying oven and allowed to cool for 10 minutes before preparing the raw materials. The inner layer (I) material A contained the following components: 2.4%-2.6% binder, 5.8%-6.0% water, and the balance iron ore powder. The outer layer (O) material B contained the following components: 2.6%-2.8% binder, 5.9%-6.0% water, and the balance iron ore powder. The mixing and homogenization time for both materials A and B was no less than 10 minutes. A binder content of 2.4% was optimal for material A, and 2.6% for material B was optimal.

[0039] Step S3: Layered briquetting experiment.

[0040] Specifically: (1) Preparation of inner layer compacts: Accurately weigh 10.0g-10.3g of raw material A and evenly fill it into a cylindrical mold cavity with an inner diameter of 20mm. Apply a linear pressure of 28-30MPa through a pressing machine, control the holding time to be 18-20s, and obtain a cylindrical inner core compact with a predetermined porosity.

[0041] (2) Composite pressing of green balls: Accurately weigh 65.0g-65.3g of raw material B, first spread 50wt% of raw material B on the bottom of an ellipsoidal mold cavity with an inner cavity size of 48×38mm, then position the core block obtained in step (1) at the central axis of the cavity, and then add the remaining 50wt% of raw material B to cover the core; use the same linear pressure (28-30MPa) and holding time (18-20s) as step (1) for secondary pressing to form a mechanical meshing interface between the inner and outer layers, and finally obtain a double-layer composite green ball with a gradient structure.

[0042] Step S4: Green ball solidification

[0043] Specifically, the double-layer composite green ball obtained in step S3 is placed in a constant temperature drying device and heat-cured in a controlled thermal environment of 100°C±2°C. The curing time is controlled within 24±0.5 hours to promote the directional migration of moisture at the interface between the inner and outer layers, thereby forming a cold-pressed pellet product with high structural stability and pore gradient distribution.

[0044] Data collection and processing: Specifically: (1) Compressive strength test: Place the solidified cold-pressed pellets in a universal testing machine, set the loading rate to 1.0±0.1 mm / min, apply an axial compressive load along the normal direction of the equatorial plane of the cold-pressed pellets, record the maximum load value at the moment of rupture of the cold-pressed pellets, and calculate the compressive strength of a single ball; (2) Bulk density determination: Mass measurement: Use an analytical balance with an accuracy of 0.01 g to weigh the pellet mass m; Volume measurement: Use the Archimedes drainage method to determine the apparent volume V of the cold-pressed pellets; Bulk density calculation: The bulk density of the cold-pressed pellets is obtained according to the formula ρ=m / V, and its value is controlled at 3.28 g / cm 3 -3.46g / cm 3 within the range.

[0045] Example 1: A method for preparing double-layer cold-pressed pellets based on a gradient binder, mainly comprising the following steps:

[0046] S1: First, the iron ore powder and metallurgical solid waste are crushed by ball milling to a particle size of ≤5mm, and then vibrated and screened through a 100-mesh (pore size 0.15mm) standard sieve. The undersize material (particle size <0.15mm) is collected as the basic raw material; the screened raw material is placed in a constant temperature drying oven and continuously dried at a constant temperature of 100±2℃ for 12±0.5h, and then cooled to room temperature (25±2℃) for use.

[0047] S2: Take 27.42g (91.4%) of dried iron ore powder and 0.78g (2.6%) of sodium silicate binder, mix them for 10 minutes, add 1.8g (6.0%) of water, and continue mixing until completely mixed to obtain raw material A for preparing the inner layer (O) briquette; take 177.45g (91%) of iron ore powder and 5.85g (3.0%) of sodium silicate binder, mix them for 10 minutes, add 11.7g (6.0%) of water, and continue mixing until completely mixed to obtain raw material B for preparing the outer layer (I) briquette.

[0048] S3: (1) Take 10g of A raw material and place it in the above-mentioned cylindrical mold, apply a linear pressure of 30MPa through a pressing machine, control the holding time to be 20s, and obtain a cylindrical core block with a predetermined porosity; (2) Weigh 65g of B raw material, first spread 50wt% of the B raw material flat on the bottom of the above-mentioned ellipsoidal mold cavity, then position the core block obtained in step (1) at the central axis of the cavity, and then add the remaining 50wt% of the B raw material to cover the core; use the same linear pressure (20MPa) and holding time (20s) as step (1) for secondary pressing to form a mechanical meshing interface between the inner and outer layers, and finally obtain a double-layer composite green ball with a gradient structure.

[0049] S4: Green pellet curing: The cold-pressed pellets obtained in step (3) are placed in a constant temperature drying device and subjected to heat curing treatment in a hot environment of 100°C. The curing time is controlled within 24 hours to obtain cold-consolidated pellet products.

[0050] S5: In the embodiment, three samples with a mass of 75 g were taken for compressive strength testing, and the measured compressive strengths were 3333.491 N, 3387.711 N and 3192.684 N, respectively, with an average value of 3304.629 N.

[0051] Example 2: A method for preparing double-layer cold-pressed pellets based on a gradient binder, mainly comprising the following steps:

[0052] S1: Same as S1 in Example 1.

[0053] S2: Take 27.48g (91.6%) of dried iron ore powder and 0.72g (2.4%) of sodium silicate binder, mix them for 10 minutes, add 1.8g (6.0%) of water, and continue to mix until completely mixed to obtain raw material A for preparing the inner layer (O) briquette; take 177.84g (91.2%) of iron ore powder and 5.46g (2.8%) of sodium silicate binder, mix them for 10 minutes, add 11.7g (6.0%) of water, and continue to mix until completely mixed to obtain raw material B for preparing the outer layer (I) briquette.

[0054] S3: Same as S3 in Example 1.

[0055] S4: Same as S4 in Example 1.

[0056] S5: In the embodiment, three samples with a mass of 75 g were taken for compressive strength testing, and the measured compressive strengths were 2626.419 N, 2546.179 N and 2379.865 N, respectively, with an average of 2517.488 N.

[0057] Example 3: A method for preparing double-layer cold-pressed pellets based on a gradient binder, mainly comprising the following steps:

[0058] S1: Same as S1 in Example 1.

[0059] S2: Take 27.54g (91.8%) of dried iron ore powder and 0.66g (2.2%) of sodium silicate binder, mix them for 10 minutes, add 1.8g (6.0%) of water, and continue to mix until completely mixed to obtain raw material A for preparing the inner layer (O) briquette; take 178.23g (91.4%) of iron ore powder and 5.07g (2.6%) of sodium silicate binder, mix them for 10 minutes, add 11.7g (6.0%) of water, and continue to mix until completely mixed to obtain raw material B for preparing the outer layer (I) briquette.

[0060] S3: Same as S3 in Example 1.

[0061] S4: Same as S4 in Example 1.

[0062] S5: In the embodiment, three samples with a mass of 75 g were taken for compressive strength testing, and the measured compressive strengths were 2185.194 N, 2312.078 N and 1987.432 N, respectively, with an average of 2161.568 N.

[0063] Compared with the cold-pressed ball preparation process in the prior art in which the binder addition amount is 3.0%-3.5%, the present invention designs a double-layer cold-pressed ball preparation method with a gradient binder distribution. The inner and outer layers use differentiated binder ratios (2.2-2.6% for the inner layer and 2.6-2.8% for the outer layer). While maintaining the compressive strength not lower than the industrial standard, the technical effect of reducing the total binder addition amount by 15% is achieved.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A double-layer cold-pressed pellet with a gradient binder, characterized by: The cold-pressed pellets are composed of a double-layer structure, including an outer layer that uses a high-density compressive protective layer with a high-proportion binder that accounts for 2.6%-3.0% of the total mass of the outer layer, and an inner layer that uses a low-proportion binder that accounts for 2.2%-2.6% of the total mass of the inner layer to construct a porous supporting skeleton, thereby achieving coordinated optimization of structural strength and raw material costs.

2. The double-layer cold-pressed pellets based on a gradient binder according to claim 1, characterized in that: The inner layer is a cylindrical core of Φ20×H10mm, and the outer layer is an ellipsoidal shell of 48×38×25mm. The cold-pressed pellets have a mass of 74.5-75.5g and a volume of 21.8-22.7cm 3 , bulk density is 3.28-3.46g / cm 3 .

3. A method for preparing double-layer cold-pressed pellets based on a gradient binder according to any one of claims 1 or 2, characterized in that: The method comprises the following steps: S1: Preparation of raw materials for pelletizing: The iron ore powder and industrial solid waste produced by the factory are crushed, sieved with a porous sieve, and particles with a size of less than 0.15 mm are selected as raw materials, and then dried; S2: Mix the raw materials, binder and water evenly: According to the different amounts of binder added to the inner and outer layers, the pelletizing materials are configured to form iron-containing mixtures, which correspond to material A and material B respectively; S3: Layered pelletizing using cold pressing process: The inner layer is made of material A, which is placed in a cylindrical mold and pressed into a cylindrical core on a press. Then half of material B is poured into an ellipsoidal mold, and the cylindrical core is placed in the center of the material layer. The remaining material B is then poured in, and pressure is applied to the ellipsoidal mold to finally obtain a green ball. S4: Cold ball consolidation: The raw balls are dried and solidified to obtain cold-pressed balls.

4. The method for preparing double-layer cold-pressed pellets based on a gradient binder according to claim 3, characterized in that: In step S1, the selected raw materials are one or more of ball-milled iron powder, iron ore powder, dust removal ash, and iron oxide scale; and the selected binder is one or more of corn starch, sodium silicate, CMC, and bentonite.

5. The method for preparing double-layer cold-pressed pellets based on a gradient binder according to claim 4, characterized in that: In step S2, when preparing the inner layer raw material, the amount of binder added accounts for 2.2%-2.6% of the total mass of material A, and the amount of water added accounts for 5.8%-6% of the total mass of material A; when preparing the outer layer raw material, the amount of binder added accounts for 2.6%-3.0% of the total mass of material B, and the amount of water added accounts for 5.9%-6% of the total mass of material A; the mixing time is 10min-15min.

6. The method for preparing double-layer cold-pressed pellets based on a gradient binder according to any one of claims 2 to 5, characterized in that: In step S3, during the cold pressing process, a linear pressure of 25-30 MPa is applied to the cylindrical mold and the ellipsoidal mold, respectively, and the holding time is maintained for 15±0.5 s to 20±0.5 s.

7. The method for preparing double-layer cold-pressed pellets based on a gradient binder according to claim 6, characterized in that: In step S4, the green balls are placed in a constant temperature environment of 100°C ± 2°C for heat curing, and the curing time is controlled to be 24 ± 0.5 hours.

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